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Pd@CeO2 core-shell nanostructures with a tunable Pd core size, shape, and nanostructure as well as a tunable CeO2 sheath thickness were obtained by a biomolecule-assisted method. The synthetic process is simple and green, as it involves only the heating of a mixture of Ce(NO3)3, l-arginine, and preformed Pd seeds in water without additives. Importantly, the synthesis is free of thiol groups and halide ions, thus providing a possible solution to the problem of secondary pollution by Pd nanoparticles in the sheath-coating process. The Pd/CeO2 nanostructures can be composited well with γ-Al2O3 to create a heterogeneous catalyst. In subsequent tests of catalytic NO reduction by CO, Pd@CeO2/Al2O3 samples based on Pd cubes (6, 10, and 18 nm), Pd octahedra (6 nm), and Pd cuboctahedra (9 nm) as well as a simply loaded Pd cube (6 nm)-CeO2/Al2O3 sample were used as catalysts to investigate the effects of the Pd core size and shape and the hybrid nanostructure on the catalytic performance. [ABSTRACT FROM AUTHOR]

Catalytic NO decomposition on LaSrMn1− xNi xO4 +δ (0 ≤ x ≤ 1) is investigated. The activity of NO decomposition increases dramatically after the substitution of Ni for Mn, but decreases when Mn is completely replaced by Ni ( x = 1.0). The optimum value is at x = 0.8. These indicate that the catalytic performance of the samples is contributed by the synergistic effect of Mn and Ni. O2-TPD and H2-TPR experiments are carried out to explain the change of activity. The former indicates that only when oxygen vacancy is created, could the catalyst show enhanced activity for NO decomposition; the latter suggests that the best activity is obtained from catalyst with the most matched redox potentials (in this work, the biggest Δ T and Δ E values). The close relationships between activity and Δ T or Δ E indicate that Δ T and Δ E are important parameters of catalyst for NO decomposition. [ABSTRACT FROM AUTHOR]

A new application of rare earth pyrophosphates in vapor phase Beckmann rearrangement of cyclohexanone oxime was investigated. The rare earth phosphates were characterized by means of XRD, FT-IR, NH3-TPD and water contact angle measurement. It was found that the weak surface acidity and appropriate surface hydrophobicity should be two key factors in the excellent performance of these catalysts. [ABSTRACT FROM AUTHOR]

• The proportion of Ostwald ripening migration of single atoms of Pt and Rh in the lean/rich oxygen alternating shift atmosphere containing CO (that is, automobile exhaust atmosphere) is close to 100 %. • Dual stable Ce-based oxides could capture and stabilize precious metals migrated due to Ostwald ripening. • The performance breakthrough was achieved and a new mechanism for improving the thermal stability of highly dispersed metal active centers under real reaction conditions was revealed. Precious metal catalysts have been widely used to catalyze various reactions, particularly three-way catalysts for automobile exhaust purification. Pt, Pd, and Rh, which are dispersed on Ce-based oxides that store and release oxygen, serve as the active center of a catalyst. However, methods to construct multifunctional three-way catalysts to maximize their efficiency and stabilize them are lacking. In this study, Ce-based oxides with a double-stable mode were synthesized to capture and stabilize the precious metals Pt and Rh migrated by Ostwald ripening (OR), and a multicomponent three-way catalyst was accurately synthesized, which showed good catalytic activity and thermal stability. The origin of Ce-based oxides with a dual-stable mode was studied by TEM, XRD, oxygen storage/release capacity and rate test, and XPS. AC-STEM, EXAFS, in situ diffuse reflectance Fourier transform infrared, and H 2 temperature-programmed reduction studied the OR migration of precious metals and the composition change after aging. Results showed that in the lean/rich oxygen alternating shift atmosphere containing CO, the proportion of OR migration of Pt and Rh precious metals whose initial state is single atoms can reach 100 %. This discovery provides a basic understanding of the sintering mechanism of precious metals, which is of great importance for the development and industrial application of three-way catalysts. Figure caption: In the lean/rich oxygen alternating shift atmosphere containing CO (automobile exhaust atmosphere), a new method for preparing super stable Pt-Rh alloy three-way catalyst from Pt and Rh single atoms was established with the help of Ostwald ripening migration mechanism. The performance breakthrough was achieved and a new mechanism for improving the thermal stability of highly dispersed metal active centers under real reaction conditions was revealed. [Display omitted] [ABSTRACT FROM AUTHOR]

• The Pt/CeO 2 nanorods catalyst was modified with three different acids for propane catalytic combustion. • Mo-modified Pt/CeO 2 catalyst converted more than 90% of propane at 300 ℃. • Pt/CeO 2 -Mo catalyst had a stronger acidic and redox capacity. • The order of reaction of Pt/CeO 2 -Mo catalyst to oxygen is −0.4, which is benefit to the adsorption of propane. • MvK mechanism the reaction followed on Pt/CeO 2 -Mo catalyst was confirmed by in situ DRIFTs. Catalytic combustion is the most commonly used reaction to purify VOCs. The activation and dissociation of the C H bond over the catalyst becomes a key factor in controlling the rate of the reaction. To identify the factors promoting C H bond decomposition and the roles played by the acidity of the catalyst in propane catalytic combustion, molybdic acid, phosphoric acid, and sulfuric acid were used to acidify CeO 2 nanorods, and Pt was then loaded onto the nanorods. The Mo acid modified Pt/CeO 2 catalyst purified more than 90% of propane at a high space velocity of 150,000 mL/(g·h) and 300 °C, which is a significant improvement over the Pt/CeO 2 catalyst. XRD patterns and TEM images showed that the crystal structure and morphology of CeO 2 were not damaged by acid modification. XPS, in situ CO-DRIFTs, NH 3 -TPD, H 2 -TPR and other characterization methods were used on Mo acid modified catalysts to explore the reasons for the improved catalytic performance. The results showed that Pt2+ and Pt4+ coexist on 1% Pt/CeO 2 -18Mo catalyst, and there are more acidic sites, redox sites and adsorbed oxygen. The reaction order test showed the reaction order of molybdic acid modified catalyst to oxygen is -0.4, which is higher than other catalysts, meaning that oxygen is difficult to inhibit the reaction on the catalyst surface. Finally, in situ DRIFTs proved that 1% Pt/CeO 2 -18Mo catalyst had strong propane adsorption and activation capacity. This catalyst provides new insight into how VOCs can be eliminated more efficiently, green and economically. [Display omitted] [ABSTRACT FROM AUTHOR]

Abstract: Catalytic reduction of NO by CO was studied over perovskite-like La2−x Sr x CuO4 (x =0.0, 0.5, 1.0) catalysts prepared by citrate method and calcined at 900°C. The catalysts were characterized by O2-TPD, H2-TPR and cyclic voltammetry (CV) measurements. Results obtained from CV were in well agreement with those obtained from O2-TPD and H2-TPR, suggesting that CV is also a powerful means in the study of heterogeneous catalytic reaction carried out at high temperatures. In O2-TPD experiment, the desorption area of β oxygen, which was contributed by the oxygen adsorbed on the oxygen vacancy, increased with the increase of Sr content and was in the same order as the activity, indicating that the activity depended largely on the oxygen vacancy resulted by Sr addition. In H2-TPR measurements, the increasing area of the first reduction peak indicating that the oxygen vacancy resulted by Sr addition plays important role in this peak, since the Cu3+ content in La1.5Sro.5CuO4 and LaSrCuO4 is the same. And in the CV curves, the area of redox peak, which represents the amount of oxygen vacancy participating in the reaction, has close correlations with the activity of NO+CO reaction, while the symmetry of redox potentials does not contribute much to the activity. Overall, with the link of oxygen vacancy, CV was introduced and has obtained great success in explaining reaction in heterogeneous catalysis. Besides, from the result that none reductive peak was observed in the first CV curves of LaSrCuO4, it suggested that the first step of a catalytic reaction is reduction, corresponding to the oxidation of catalyst i.e., M n+(Cu2+)→M(n+1)+(Cu3+). [Copyright &y& Elsevier]